The following abbreviations are herewith defined:
3GPP third generation partnership project
AMC adaptive modulation and coding
AT allocation table
BS base station
DCH dedicated transport channel
DL downlink (Node B to UE)
eNode B evolved Node B
H-ARQ hybrid automatic repeat request
HSUPA high speed uplink packet access
L1 layer 1 (physical (PHY) Layer)
LTE long term evolution
Node B base station
OFDMA orthogonal frequency division multiple access
RACH random access channel
RF radio frequency
RRC radio resource control
SC-FDMA single carrier-frequency division multiple access
SCH shared transport channel
TTI transmission time interval
UE user equipment
UL uplink (UE to Node B)
UMTS universal mobile telecommunications system
UTRA universal terrestrial radio access
UTRAN universal terrestrial radio access network
E-UTRAN evolved UTRAN
QoS quality of service
The following references contain information of use in understanding exemplary embodiments of the disclosed invention: third generation partnership project (3GPP) technical report (TR) 25.913, V7.2.0 (2005-12), Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN); 3GPP TR 25.814, V0.5.0 (2005-11), Physical Layer Aspects for Evolved UTRA; and 3GPP TSG RAN WG1 Meeting #42bis, San Diego, USA, 10-14 Oct., 2005, “DL resource allocation considerations” (R1-051090).
Of particular interest to the exemplary embodiments of this invention are modern cellular networks, such as one referred to as UTRA LTE in 3GPP UMTS. Modern cellular networks may employ multi-carrier technologies such as OFDMA in the DL and SC FDMA in the UL, and various advanced radio transmission techniques such as AMC and H-ARQ. The radio interface relies on the presence of a SCH in both the UL and DL with fast adaptive resource allocation for simple and efficient radio resource utilization and QoS support, and no longer uses a DCH. Details of this particular type of system may be found in 3GPP TR 25.913 and 3GPP TR 25.814.
In such a system, in order for an active UE and a serving BS to transmit and receive user data in both the UL and DL, the UE and the BS must be in synchronization with each other, and the UE must be informed of dedicated resources, including allowed transport formats, for its next TTI prior to the start of the TTI.
In the DL, the UE is able to acquire the synchronization whenever needed by “listening” to DL pilot and broadcast channels. In the UL, however, the situation is more complex, and the UE may need to adjust its transmission timing based on timing advance information feedback from the BS. An initial UL synchronization between the UE and the BS often requires using a RACH. As is known, the RACH is a logical channel and is a contention-based access channel that is used by UEs to transmit control messages and requests. However, the use of a contention-based channel implies that collisions with other UEs can occur, resulting in some finite and variable access delay. This initial UL synchronization procedure may also be referred to in the literature as a ranging process.
Consider now a situation in which the UE has an urgent need to (re)establish the UL synchronization with the BS in order to communicate for further transactions known and, perhaps, controlled by the network. As an example, the UE may be in a handover process between two base stations, i.e., between a source BS (current cell) and a target BS (next cell), as illustrated in FIG. 2. The circled UE transaction in FIG. 2, labeled “Detach from old cell, and synchronize to new cell” indicates a relevant situation in which the UE must quickly establish the UL synchronization with the target BS (shown as “Target eNB”, also known as a target eNode B, in FIG. 2). As another example, consider a case in which the BS needs to page the UE, which is in an idle state, for an incoming call. Depending on UE mobility and network deployment scenarios, the network knows the exact UE location on a cell basis (for example, in a fixed wireless and/or single cell system). In this case the UE, after receiving the paging message, has an urgent need to establish the radio connection with the BS and, in order to accomplish this task, is required to first perform UL synchronization. As yet another example, consider a case where the UE is in an active state and for some reason related to radio channel conditions loses synchronization with the BS in the UL. The UE must then re-establish the UL synchronization as soon as possible.
As can be appreciated, the various exemplary cases considered above have in common an urgent need for the UE to perform a fast and reliable connection and/or (re)establishment of UL synchronization with the BS, and the network is aware of and able to control the UE in the DL.
In current cellular systems, the UE in the aforementioned situations needs to perform the ranging procedure using the RACH toward the target BS to acquire advance timing information and synchronization in the UL. However, and as was noted above, the RACH is a contention channel and therefore collisions with other UEs can occur, resulting in a user-perceivable and undesirable access delay.
It should be noted that E UTRAN has a much more stringent latency requirement than UTRAN, yet more flexibility in terms of SCH resource allocation and utilization for both the UL and the DL on a L1 sub frame basis. This is accomplished through the use of the AT that is broadcast in the DL at the beginning of each L1 sub frame for all active UEs. The principles and general requirements of resource allocation and related signaling for LTE of UTRA (E UTRA) are provided, for example, in 3GPP TR 25.814 and in R1 051090.